In general, Al atoms in Al and Al alloy wiring used for semiconductor devices migrate too easily even at relatively low temperatures as in the range of 100 to 200.degree. C., because the melting point of Al is low. Therefore, when electric current flows in Al and Al alloy wiring, electro-migration and stress migration because of thermal stress loading occur. This causes a breaking of the wire. That is one of the major factors which lowers the reliability of semiconductor devices.
Therefore, various means of evaluation have been developed to solve the shortfalls of this migration. For example, a scanning ion microscope (hereinafter referred to as "SIM") and a transmission electron microscope (hereinafter referred to as "TEM") are being used for observation and structural analysis of crystal grains in Al and Al alloy wiring.
However, in the case of the TEM, a great amount of time and labor are required to make samples. In addition, with semiconductor devices having become more minute and highly integrated, Al wiring has become laminated and making the samples has become more difficult. In the case of the SIM, since the SIM scans ions with a large atomic radius, the resolution of images obtained is not very high and observation of minute crystal grains in Al wiring has been difficult.